<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019f0498-e110-764b-a2d7-6a8f25676695,g:1285fca4-b249-44a6-a266-f74106f2bcd4-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:coll="http://www.collegiumpharma.com/20260630" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:dtr-types="http://www.xbrl.org/dtr/type/2024-01-31" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.collegiumpharma.com/20260630">
  <xs:import namespace="http://fasb.org/srt/2026" schemaLocation="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd"/>
  <xs:import namespace="http://fasb.org/us-gaap/2026" schemaLocation="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/dtr/type/2024-01-31" schemaLocation="https://www.xbrl.org/dtr/type/2024-01-31/types.xsd"/>
  <xs:import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/dei/2026" schemaLocation="https://xbrl.sec.gov/dei/2026/dei-2026.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/ecd/2026" schemaLocation="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd"/>
  <xs:annotation>
    <xs:appinfo>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="coll-20260630_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="coll-20260630_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="coll-20260630_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="coll-20260630_cal.xml" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:type="simple"/>
      <link:roleType id="Cover" roleURI="http://www.collegiumpharma.com/role/Cover">
        <link:definition>0000001 - Document - Cover</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CONDENSEDCONSOLIDATEDBALANCESHEETSUNAUDITED" roleURI="http://www.collegiumpharma.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSUNAUDITED">
        <link:definition>9952151 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CONDENSEDCONSOLIDATEDBALANCESHEETSUNAUDITEDParenthetical" roleURI="http://www.collegiumpharma.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSUNAUDITEDParenthetical">
        <link:definition>9952152 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONSUNAUDITED" roleURI="http://www.collegiumpharma.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONSUNAUDITED">
        <link:definition>9952153 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMELOSSUNAUDITED" roleURI="http://www.collegiumpharma.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMELOSSUNAUDITED">
        <link:definition>9952154 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (UNAUDITED)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUNAUDITED" roleURI="http://www.collegiumpharma.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUNAUDITED">
        <link:definition>9952155 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="NatureofBusiness" roleURI="http://www.collegiumpharma.com/role/NatureofBusiness">
        <link:definition>9952156 - Disclosure - Nature of Business</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPolicies" roleURI="http://www.collegiumpharma.com/role/SummaryofSignificantAccountingPolicies">
        <link:definition>9952157 - Disclosure - Summary of Significant Accounting Policies</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenuefromContractswithCustomers" roleURI="http://www.collegiumpharma.com/role/RevenuefromContractswithCustomers">
        <link:definition>9952158 - Disclosure - Revenue from Contracts with Customers</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Acquisition" roleURI="http://www.collegiumpharma.com/role/Acquisition">
        <link:definition>9952159 - Disclosure - Acquisition</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LicenseAgreements" roleURI="http://www.collegiumpharma.com/role/LicenseAgreements">
        <link:definition>9952160 - Disclosure - License Agreements</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EarningsPerShare" roleURI="http://www.collegiumpharma.com/role/EarningsPerShare">
        <link:definition>9952161 - Disclosure - Earnings Per Share</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueofFinancialInstruments" roleURI="http://www.collegiumpharma.com/role/FairValueofFinancialInstruments">
        <link:definition>9952162 - Disclosure - Fair Value of Financial Instruments</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="MarketableSecurities" roleURI="http://www.collegiumpharma.com/role/MarketableSecurities">
        <link:definition>9952163 - Disclosure - Marketable Securities</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Inventory" roleURI="http://www.collegiumpharma.com/role/Inventory">
        <link:definition>9952164 - Disclosure - Inventory</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillandIntangibleAssets" roleURI="http://www.collegiumpharma.com/role/GoodwillandIntangibleAssets">
        <link:definition>9952165 - Disclosure - Goodwill and Intangible Assets</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AccruedLiabilities" roleURI="http://www.collegiumpharma.com/role/AccruedLiabilities">
        <link:definition>9952166 - Disclosure - Accrued Liabilities</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="TermNotesPayable" roleURI="http://www.collegiumpharma.com/role/TermNotesPayable">
        <link:definition>9952167 - Disclosure - Term Notes Payable</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConvertibleSeniorNotes" roleURI="http://www.collegiumpharma.com/role/ConvertibleSeniorNotes">
        <link:definition>9952168 - Disclosure - Convertible Senior Notes</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DeferredRoyaltyObligation" roleURI="http://www.collegiumpharma.com/role/DeferredRoyaltyObligation">
        <link:definition>9952169 - Disclosure - Deferred Royalty Obligation</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Equity" roleURI="http://www.collegiumpharma.com/role/Equity">
        <link:definition>9952170 - Disclosure - Equity</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockbasedCompensation" roleURI="http://www.collegiumpharma.com/role/StockbasedCompensation">
        <link:definition>9952171 - Disclosure - Stock-based Compensation</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommitmentsandContingencies" roleURI="http://www.collegiumpharma.com/role/CommitmentsandContingencies">
        <link:definition>9952172 - Disclosure - Commitments and Contingencies</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxes" roleURI="http://www.collegiumpharma.com/role/IncomeTaxes">
        <link:definition>9952173 - Disclosure - Income Taxes</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentInformation" roleURI="http://www.collegiumpharma.com/role/SegmentInformation">
        <link:definition>9952174 - Disclosure - Segment Information</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SubsequentEvents" roleURI="http://www.collegiumpharma.com/role/SubsequentEvents">
        <link:definition>9952175 - Disclosure - Subsequent Events</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPoliciesPolicies" roleURI="http://www.collegiumpharma.com/role/SummaryofSignificantAccountingPoliciesPolicies">
        <link:definition>9955511 - Disclosure - Summary of Significant Accounting Policies (Policies)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenuefromContractswithCustomersTables" roleURI="http://www.collegiumpharma.com/role/RevenuefromContractswithCustomersTables">
        <link:definition>9955512 - Disclosure - Revenue from Contracts with Customers (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionTables" roleURI="http://www.collegiumpharma.com/role/AcquisitionTables">
        <link:definition>9955513 - Disclosure - Acquisition (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EarningsPerShareTables" roleURI="http://www.collegiumpharma.com/role/EarningsPerShareTables">
        <link:definition>9955514 - Disclosure - Earnings Per Share (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueofFinancialInstrumentsTables" roleURI="http://www.collegiumpharma.com/role/FairValueofFinancialInstrumentsTables">
        <link:definition>9955515 - Disclosure - Fair Value of Financial Instruments (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="MarketableSecuritiesTables" roleURI="http://www.collegiumpharma.com/role/MarketableSecuritiesTables">
        <link:definition>9955516 - Disclosure - Marketable Securities (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="InventoryTables" roleURI="http://www.collegiumpharma.com/role/InventoryTables">
        <link:definition>9955517 - Disclosure - Inventory (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillandIntangibleAssetsTables" roleURI="http://www.collegiumpharma.com/role/GoodwillandIntangibleAssetsTables">
        <link:definition>9955518 - Disclosure - Goodwill and Intangible Assets (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AccruedLiabilitiesTables" roleURI="http://www.collegiumpharma.com/role/AccruedLiabilitiesTables">
        <link:definition>9955519 - Disclosure - Accrued Liabilities (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="TermNotesPayableTables" roleURI="http://www.collegiumpharma.com/role/TermNotesPayableTables">
        <link:definition>9955520 - Disclosure - Term Notes Payable (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConvertibleSeniorNotesTables" roleURI="http://www.collegiumpharma.com/role/ConvertibleSeniorNotesTables">
        <link:definition>9955521 - Disclosure - Convertible Senior Notes (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DeferredRoyaltyObligationTables" roleURI="http://www.collegiumpharma.com/role/DeferredRoyaltyObligationTables">
        <link:definition>9955522 - Disclosure - Deferred Royalty Obligation (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EquityTables" roleURI="http://www.collegiumpharma.com/role/EquityTables">
        <link:definition>9955523 - Disclosure - Equity (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockbasedCompensationTables" roleURI="http://www.collegiumpharma.com/role/StockbasedCompensationTables">
        <link:definition>9955524 - Disclosure - Stock-based Compensation (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesTables" roleURI="http://www.collegiumpharma.com/role/IncomeTaxesTables">
        <link:definition>9955525 - Disclosure - Income Taxes (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentInformationTables" roleURI="http://www.collegiumpharma.com/role/SegmentInformationTables">
        <link:definition>9955526 - Disclosure - Segment Information (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenuefromContractswithCustomersNarrativeDetails" roleURI="http://www.collegiumpharma.com/role/RevenuefromContractswithCustomersNarrativeDetails">
        <link:definition>9955527 - Disclosure - Revenue from Contracts with Customers - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenuefromContractswithCustomersScheduleofProductRevenueProvisionandAllowanceCategoriesDetails" roleURI="http://www.collegiumpharma.com/role/RevenuefromContractswithCustomersScheduleofProductRevenueProvisionandAllowanceCategoriesDetails">
        <link:definition>9955528 - Disclosure - Revenue from Contracts with Customers - Schedule of Product Revenue Provision and Allowance Categories (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenuefromContractswithCustomersScheduleofDisaggregationofRevenueDetails" roleURI="http://www.collegiumpharma.com/role/RevenuefromContractswithCustomersScheduleofDisaggregationofRevenueDetails">
        <link:definition>9955529 - Disclosure - Revenue from Contracts with Customers - Schedule of Disaggregation of Revenue (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionNarrativeDetails" roleURI="http://www.collegiumpharma.com/role/AcquisitionNarrativeDetails">
        <link:definition>9955530 - Disclosure - Acquisition - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionScheduleofConsiderationPaidforAcquisitionDetails" roleURI="http://www.collegiumpharma.com/role/AcquisitionScheduleofConsiderationPaidforAcquisitionDetails">
        <link:definition>9955531 - Disclosure - Acquisition - Schedule of Consideration Paid for Acquisition (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionScheduleofAllocationofAcquisitionPurchasePriceDetails" roleURI="http://www.collegiumpharma.com/role/AcquisitionScheduleofAllocationofAcquisitionPurchasePriceDetails">
        <link:definition>9955532 - Disclosure - Acquisition - Schedule of Allocation of Acquisition Purchase Price (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionScheduleofUnauditedProFormaSummaryofOperationsDetails" roleURI="http://www.collegiumpharma.com/role/AcquisitionScheduleofUnauditedProFormaSummaryofOperationsDetails">
        <link:definition>9955533 - Disclosure - Acquisition - Schedule of Unaudited Pro Forma Summary of Operations (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionScheduleofAcquisitionRelatedExpensesDetails" roleURI="http://www.collegiumpharma.com/role/AcquisitionScheduleofAcquisitionRelatedExpensesDetails">
        <link:definition>9955534 - Disclosure - Acquisition - Schedule of Acquisition Related Expenses (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LicenseAgreementsDetails" roleURI="http://www.collegiumpharma.com/role/LicenseAgreementsDetails">
        <link:definition>9955535 - Disclosure - License Agreements (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LicenseAgreementsDetails_1" roleURI="http://www.collegiumpharma.com/role/LicenseAgreementsDetails_1">
        <link:definition>9955535 - Disclosure - License Agreements (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EarningsPerShareScheduleofComputationsofBasicandDilutedNetLossPerShareDetails" roleURI="http://www.collegiumpharma.com/role/EarningsPerShareScheduleofComputationsofBasicandDilutedNetLossPerShareDetails">
        <link:definition>9955536 - Disclosure - Earnings Per Share - Schedule of Computations of Basic and Diluted Net (Loss) Per Share (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EarningsPerShareScheduleofDilutiveSecuritiesExcludedfromtheCalculationofDilutedEarningsPerShareDetails" roleURI="http://www.collegiumpharma.com/role/EarningsPerShareScheduleofDilutiveSecuritiesExcludedfromtheCalculationofDilutedEarningsPerShareDetails">
        <link:definition>9955537 - Disclosure - Earnings Per Share - Schedule of Dilutive Securities Excluded from the Calculation of Diluted Earnings Per Share (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueofFinancialInstrumentsScheduleofFinancialInstrumentsMeasuredatFairValuebyLevelWithinFairValueHierarchyDetails" roleURI="http://www.collegiumpharma.com/role/FairValueofFinancialInstrumentsScheduleofFinancialInstrumentsMeasuredatFairValuebyLevelWithinFairValueHierarchyDetails">
        <link:definition>9955538 - Disclosure - Fair Value of Financial Instruments - Schedule of Financial Instruments Measured at Fair Value by Level Within Fair Value Hierarchy (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueofFinancialInstrumentsNarrativeDetails" roleURI="http://www.collegiumpharma.com/role/FairValueofFinancialInstrumentsNarrativeDetails">
        <link:definition>9955539 - Disclosure - Fair Value of Financial Instruments - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueofFinancialInstrumentsScheduleofSignificantUnobservableInputsUsedInTheFairValueMeasurementsDetails" roleURI="http://www.collegiumpharma.com/role/FairValueofFinancialInstrumentsScheduleofSignificantUnobservableInputsUsedInTheFairValueMeasurementsDetails">
        <link:definition>9955540 - Disclosure - Fair Value of Financial Instruments - Schedule of Significant Unobservable Inputs Used In The Fair Value Measurements (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueofFinancialInstrumentsScheduleofReconciliationofBeginningandEndingBalancesRelatedtotheContingentConsiderationDetails" roleURI="http://www.collegiumpharma.com/role/FairValueofFinancialInstrumentsScheduleofReconciliationofBeginningandEndingBalancesRelatedtotheContingentConsiderationDetails">
        <link:definition>9955541 - Disclosure - Fair Value of Financial Instruments - Schedule of Reconciliation of Beginning and Ending Balances Related to the Contingent Consideration (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="MarketableSecuritiesScheduleofAvailableforSaleSecuritiesonBalanceSheetDetails" roleURI="http://www.collegiumpharma.com/role/MarketableSecuritiesScheduleofAvailableforSaleSecuritiesonBalanceSheetDetails">
        <link:definition>9955542 - Disclosure - Marketable Securities - Schedule of Available-for-Sale Securities on Balance Sheet (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="MarketableSecuritiesScheduleofAvailableforSaleSecuritiesonBalanceSheetDetails_1" roleURI="http://www.collegiumpharma.com/role/MarketableSecuritiesScheduleofAvailableforSaleSecuritiesonBalanceSheetDetails_1">
        <link:definition>9955542 - Disclosure - Marketable Securities - Schedule of Available-for-Sale Securities on Balance Sheet (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="MarketableSecuritiesScheduleofAvailableforSaleDebtSecuritiesDetails" roleURI="http://www.collegiumpharma.com/role/MarketableSecuritiesScheduleofAvailableforSaleDebtSecuritiesDetails">
        <link:definition>9955543 - Disclosure - Marketable Securities - Schedule of Available-for-Sale Debt Securities (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="MarketableSecuritiesScheduleofContractualMaturitiesofAvailableforSaleSecuritiesOtherthanInvestmentsDetails" roleURI="http://www.collegiumpharma.com/role/MarketableSecuritiesScheduleofContractualMaturitiesofAvailableforSaleSecuritiesOtherthanInvestmentsDetails">
        <link:definition>9955544 - Disclosure - Marketable Securities - Schedule of Contractual Maturities of Available-for-Sale Securities Other than Investments (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="MarketableSecuritiesNarrativeDetails" roleURI="http://www.collegiumpharma.com/role/MarketableSecuritiesNarrativeDetails">
        <link:definition>9955545 - Disclosure - Marketable Securities - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="InventoryScheduleofInventoryDetails" roleURI="http://www.collegiumpharma.com/role/InventoryScheduleofInventoryDetails">
        <link:definition>9955546 - Disclosure - Inventory - Schedule of Inventory (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="InventoryScheduleofBalanceSheetClassificationofInventoryDetails" roleURI="http://www.collegiumpharma.com/role/InventoryScheduleofBalanceSheetClassificationofInventoryDetails">
        <link:definition>9955547 - Disclosure - Inventory - Schedule of Balance Sheet Classification of Inventory (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillandIntangibleAssetsNarrativeDetails" roleURI="http://www.collegiumpharma.com/role/GoodwillandIntangibleAssetsNarrativeDetails">
        <link:definition>9955548 - Disclosure - Goodwill and Intangible Assets - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillandIntangibleAssetsScheduleofCostAccumulatedAmortizationandCarryingAmountofIntangibleAssetsDetails" roleURI="http://www.collegiumpharma.com/role/GoodwillandIntangibleAssetsScheduleofCostAccumulatedAmortizationandCarryingAmountofIntangibleAssetsDetails">
        <link:definition>9955549 - Disclosure - Goodwill and Intangible Assets - Schedule of Cost, Accumulated Amortization and Carrying Amount of Intangible Assets (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillandIntangibleAssetsScheduleofAmortizationandImpairmentExpenseDetails" roleURI="http://www.collegiumpharma.com/role/GoodwillandIntangibleAssetsScheduleofAmortizationandImpairmentExpenseDetails">
        <link:definition>9955550 - Disclosure - Goodwill and Intangible Assets - Schedule of Amortization and Impairment Expense (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillandIntangibleAssetsScheduleofFutureAmortizationExpensesDetails" roleURI="http://www.collegiumpharma.com/role/GoodwillandIntangibleAssetsScheduleofFutureAmortizationExpensesDetails">
        <link:definition>9955551 - Disclosure - Goodwill and Intangible Assets - Schedule of Future Amortization Expenses (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AccruedLiabilitiesDetails" roleURI="http://www.collegiumpharma.com/role/AccruedLiabilitiesDetails">
        <link:definition>9955552 - Disclosure - Accrued Liabilities (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="TermNotesPayableNarrativeDetails" roleURI="http://www.collegiumpharma.com/role/TermNotesPayableNarrativeDetails">
        <link:definition>9955553 - Disclosure - Term Notes Payable - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="TermNotesPayableScheduleofTotalInterestExpenseRecognizedDetails" roleURI="http://www.collegiumpharma.com/role/TermNotesPayableScheduleofTotalInterestExpenseRecognizedDetails">
        <link:definition>9955554 - Disclosure - Term Notes Payable - Schedule of Total Interest Expense Recognized (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="TermNotesPayableScheduleofPrincipalRepaymentsofDebtDetails" roleURI="http://www.collegiumpharma.com/role/TermNotesPayableScheduleofPrincipalRepaymentsofDebtDetails">
        <link:definition>9955555 - Disclosure - Term Notes Payable - Schedule of Principal Repayments of Debt (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConvertibleSeniorNotesNarrativeDetails" roleURI="http://www.collegiumpharma.com/role/ConvertibleSeniorNotesNarrativeDetails">
        <link:definition>9955556 - Disclosure - Convertible Senior Notes - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConvertibleSeniorNotesScheduleofConvertibleNotesOutstandingDetails" roleURI="http://www.collegiumpharma.com/role/ConvertibleSeniorNotesScheduleofConvertibleNotesOutstandingDetails">
        <link:definition>9955557 - Disclosure - Convertible Senior Notes - Schedule of Convertible Notes Outstanding (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConvertibleSeniorNotesScheduleofPrincipalRepaymentsofDebtDetails" roleURI="http://www.collegiumpharma.com/role/ConvertibleSeniorNotesScheduleofPrincipalRepaymentsofDebtDetails">
        <link:definition>9955558 - Disclosure - Convertible Senior Notes - Schedule of Principal Repayments of Debt (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConvertibleSeniorNotesScheduleofTotalInterestExpenseRecognizedDetails" roleURI="http://www.collegiumpharma.com/role/ConvertibleSeniorNotesScheduleofTotalInterestExpenseRecognizedDetails">
        <link:definition>9955559 - Disclosure - Convertible Senior Notes - Schedule of Total Interest Expense Recognized (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DeferredRoyaltyObligationNarrativeDetails" roleURI="http://www.collegiumpharma.com/role/DeferredRoyaltyObligationNarrativeDetails">
        <link:definition>9955560 - Disclosure - Deferred Royalty Obligation -Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DeferredRoyaltyObligationScheduleofDeferredRoyaltyObligationDetails" roleURI="http://www.collegiumpharma.com/role/DeferredRoyaltyObligationScheduleofDeferredRoyaltyObligationDetails">
        <link:definition>9955561 - Disclosure - Deferred Royalty Obligation - Schedule of Deferred Royalty Obligation (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EquityScheduleofChangesinShareholdersEquityDetails" roleURI="http://www.collegiumpharma.com/role/EquityScheduleofChangesinShareholdersEquityDetails">
        <link:definition>9955562 - Disclosure - Equity - Schedule of Changes in Shareholders' Equity (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EquityNarrativeDetails" roleURI="http://www.collegiumpharma.com/role/EquityNarrativeDetails">
        <link:definition>9955563 - Disclosure - Equity - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockbasedCompensationScheduleofShareUnitsActivityDetails" roleURI="http://www.collegiumpharma.com/role/StockbasedCompensationScheduleofShareUnitsActivityDetails">
        <link:definition>9955564 - Disclosure - Stock-based Compensation - Schedule of Share Units Activity (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockbasedCompensationNarrativeDetails" roleURI="http://www.collegiumpharma.com/role/StockbasedCompensationNarrativeDetails">
        <link:definition>9955565 - Disclosure - Stock-based Compensation - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockbasedCompensationNarrativeDetails_1" roleURI="http://www.collegiumpharma.com/role/StockbasedCompensationNarrativeDetails_1">
        <link:definition>9955565 - Disclosure - Stock-based Compensation - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockbasedCompensationScheduleofStockOptionActivityDetails" roleURI="http://www.collegiumpharma.com/role/StockbasedCompensationScheduleofStockOptionActivityDetails">
        <link:definition>9955566 - Disclosure - Stock-based Compensation - Schedule of Stock Option Activity (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommitmentsandContingenciesDetails" roleURI="http://www.collegiumpharma.com/role/CommitmentsandContingenciesDetails">
        <link:definition>9955567 - Disclosure - Commitments and Contingencies (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesDetails" roleURI="http://www.collegiumpharma.com/role/IncomeTaxesDetails">
        <link:definition>9955568 - Disclosure - Income Taxes (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentInformationNarrativeDetails" roleURI="http://www.collegiumpharma.com/role/SegmentInformationNarrativeDetails">
        <link:definition>9955569 - Disclosure - Segment Information - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentInformationScheduleofSegmentInformationDetails" roleURI="http://www.collegiumpharma.com/role/SegmentInformationScheduleofSegmentInformationDetails">
        <link:definition>9955570 - Disclosure - Segment Information - Schedule of Segment Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SubsequentEventsDetails" roleURI="http://www.collegiumpharma.com/role/SubsequentEventsDetails">
        <link:definition>9955571 - Disclosure - Subsequent Events (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
    </xs:appinfo>
  </xs:annotation>
  <xs:element id="coll_AccruedRebatesReturnsAndDiscountsCurrent" abstract="false" name="AccruedRebatesReturnsAndDiscountsCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationConsiderationLiabilityCurrent" abstract="false" name="BusinessCombinationConsiderationLiabilityCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_DeferredRoyaltyLiabilityNonCurrent" abstract="false" name="DeferredRoyaltyLiabilityNonCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_OperatingLeasePaymentsNonCash" abstract="false" name="OperatingLeasePaymentsNonCash" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_NetAmortizationAccretionForDeferredRoyaltyObligation" abstract="false" name="NetAmortizationAccretionForDeferredRoyaltyObligation" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_IncreaseDecreaseInAccruedRebatesReturnsAndDiscounts" abstract="false" name="IncreaseDecreaseInAccruedRebatesReturnsAndDiscounts" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_ContingentConsiderationFairValueDisclosureClassifiedAsNonCashActivity" abstract="false" name="ContingentConsiderationFairValueDisclosureClassifiedAsNonCashActivity" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_LicensesAgreementsAbstract" abstract="true" name="LicensesAgreementsAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="coll_LicenseAgreementsTextBlock" abstract="false" name="LicenseAgreementsTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="coll_ConvertibleSeniorNotes.Abstract" abstract="true" name="ConvertibleSeniorNotes.Abstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="coll_ConvertibleSeniorNotesDisclosureTextBlock" abstract="false" name="ConvertibleSeniorNotesDisclosureTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="coll_DeferredRoyaltyObligationAbstract" abstract="true" name="DeferredRoyaltyObligationAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="coll_DeferredRoyaltyObligationTextBlock" abstract="false" name="DeferredRoyaltyObligationTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="coll_SummaryOfProductRevenueProvisionAndAllowanceCategoriesTableTextBlock" abstract="false" name="SummaryOfProductRevenueProvisionAndAllowanceCategoriesTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="coll_ScheduleOfConsiderationPaidTableTextBlock" abstract="false" name="ScheduleOfConsiderationPaidTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="coll_BusinessCombinationAcquisitionRelatedExpensesTableTextBlock" abstract="false" name="BusinessCombinationAcquisitionRelatedExpensesTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="coll_ScheduleOfInventoryBalanceSheetClassificationTableTextBlock" abstract="false" name="ScheduleOfInventoryBalanceSheetClassificationTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="coll_ScheduleOfInterestExpenseRecognizedOnConvertibleNotesTableTextBlock" abstract="false" name="ScheduleOfInterestExpenseRecognizedOnConvertibleNotesTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="coll_ScheduleOfDeferredRoyaltyObligationTableTextBlock" abstract="false" name="ScheduleOfDeferredRoyaltyObligationTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="coll_PaymentReceivedTerm" abstract="false" name="PaymentReceivedTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="coll_ReturnsPolicyThresholdProductReturnPeriod" abstract="false" name="ReturnsPolicyThresholdProductReturnPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="coll_ReturnsPolicyThresholdProductReturnPeriodPriorToExpiration" abstract="false" name="ReturnsPolicyThresholdProductReturnPeriodPriorToExpiration" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="coll_ReturnsPolicyThresholdProductReturnPeriodAfterExpiration" abstract="false" name="ReturnsPolicyThresholdProductReturnPeriodAfterExpiration" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="coll_ContractWithCustomerUpfrontPayment" abstract="false" name="ContractWithCustomerUpfrontPayment" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_AllowanceForRebatesAndIncentivesMember" abstract="true" name="AllowanceForRebatesAndIncentivesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_ContractWithCustomerRefundLiabilityMember" abstract="true" name="ContractWithCustomerRefundLiabilityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_AllowanceAndChargebacksForTradeReceivablesMember" abstract="true" name="AllowanceAndChargebacksForTradeReceivablesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_MovementInContractWithCustomerLiabilityRollForward" abstract="true" name="MovementInContractWithCustomerLiabilityRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="coll_ContractWithCustomerLiabilityProvisionForCurrentPeriodSales" abstract="false" name="ContractWithCustomerLiabilityProvisionForCurrentPeriodSales" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_ContractWithCustomerLiabilityChangeInEstimateOfPriorPeriodSales" abstract="false" name="ContractWithCustomerLiabilityChangeInEstimateOfPriorPeriodSales" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_ContractWithCustomerLiabilityDecreaseDueToCreditsAndPayments" abstract="false" name="ContractWithCustomerLiabilityDecreaseDueToCreditsAndPayments" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BelbucaMember" abstract="true" name="BelbucaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_XtampzaERMember" abstract="true" name="XtampzaERMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_JornayPmMember" abstract="true" name="JornayPmMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_NucyntaIRMember" abstract="true" name="NucyntaIRMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_NucyntaERMember" abstract="true" name="NucyntaERMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_AzstarysMember" abstract="true" name="AzstarysMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_SymproicMember" abstract="true" name="SymproicMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_NucyntaERAGMember" abstract="true" name="NucyntaERAGMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_NucyntaIRAGMember" abstract="true" name="NucyntaIRAGMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_AZSTARYSAcquisitionMember" abstract="true" name="AZSTARYSAcquisitionMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_IronshoreAcquisitionMember" abstract="true" name="IronshoreAcquisitionMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_A2025CreditAgreementMember" abstract="true" name="A2025CreditAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_PaymentsToAcquireBusinessesGrossExisting" abstract="false" name="PaymentsToAcquireBusinessesGrossExisting" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationMaximumAggregateMilestonePayments" abstract="false" name="BusinessCombinationMaximumAggregateMilestonePayments" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_EscrowDepositReleasePeriodAfterAcquisitionDate" abstract="false" name="EscrowDepositReleasePeriodAfterAcquisitionDate" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="coll_EscrowDepositReleasePeriodAfterClosingDate" abstract="false" name="EscrowDepositReleasePeriodAfterClosingDate" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="coll_BusinessCombinationIncreaseDecreaseInInventoryDueToPurchaseAccountingAdjustments" abstract="false" name="BusinessCombinationIncreaseDecreaseInInventoryDueToPurchaseAccountingAdjustments" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationReductionInConsiderationPayable" abstract="false" name="BusinessCombinationReductionInConsiderationPayable" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccruals" abstract="false" name="BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccruals" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxAssets" abstract="false" name="BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxAssets" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentCertainOtherAccounts" abstract="false" name="BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentCertainOtherAccounts" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationConsiderationTransferredCashHeldInEscrow" abstract="false" name="BusinessCombinationConsiderationTransferredCashHeldInEscrow" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationConsiderationTransferredDeferredConsideration" abstract="false" name="BusinessCombinationConsiderationTransferredDeferredConsideration" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationConsiderationTransferredContingentConsideration" abstract="false" name="BusinessCombinationConsiderationTransferredContingentConsideration" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationOtherPurchaseConsiderationPayable" abstract="false" name="BusinessCombinationOtherPurchaseConsiderationPayable" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseAssets" abstract="false" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseAssets" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedExpenses" abstract="false" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedExpenses" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedRebatesReturnsAndDiscounts" abstract="false" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedRebatesReturnsAndDiscounts" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBorrowings" abstract="false" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBorrowings" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseLiabilities" abstract="false" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseLiabilities" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSeniorSecuredNotesPayable" abstract="false" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSeniorSecuredNotesPayable" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredRoyaltyLiability" abstract="false" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredRoyaltyLiability" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationLegalDefenseExpenses" abstract="false" name="BusinessCombinationLegalDefenseExpenses" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationEmployeeRelatedExpenses" abstract="false" name="BusinessCombinationEmployeeRelatedExpenses" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationTransactionCosts" abstract="false" name="BusinessCombinationTransactionCosts" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_BusinessCombinationOtherAcquisitionExpenses" abstract="false" name="BusinessCombinationOtherAcquisitionExpenses" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_LicenseAgreementsTable" abstract="true" name="LicenseAgreementsTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="coll_GrunenthalLicenseMember" abstract="true" name="GrunenthalLicenseMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_ShionogiLicenseAndSupplyAgreementMember" abstract="true" name="ShionogiLicenseAndSupplyAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_ArkBioLicenseAgreementMember" abstract="true" name="ArkBioLicenseAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_LicenseAgreementsLineItems" abstract="true" name="LicenseAgreementsLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="coll_LicenseAgreementRoyaltyPercentage" abstract="false" name="LicenseAgreementRoyaltyPercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="coll_LicenseAgreementAdditionalPercentageOfNetSalesOnPassThroughBasisPayableToThirdPartyLicensor" abstract="false" name="LicenseAgreementAdditionalPercentageOfNetSalesOnPassThroughBasisPayableToThirdPartyLicensor" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="coll_LicenseTerm" abstract="false" name="LicenseTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="coll_PotentialProceedsFromSalesBasedMilestonePayments" abstract="false" name="PotentialProceedsFromSalesBasedMilestonePayments" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_EmployeeStockPurchasePlanMember" abstract="true" name="EmployeeStockPurchasePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_ContingentConsiderationLiabilityMember" abstract="true" name="ContingentConsiderationLiabilityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_TwoPointEightSevenFiveConvertibleSeniorNotesDue2029Member" abstract="true" name="TwoPointEightSevenFiveConvertibleSeniorNotesDue2029Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_DeferredRoyaltyObligationFairValue" abstract="false" name="DeferredRoyaltyObligationFairValue" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_MeasurementInputProbabilityOfPaymentMember" abstract="true" name="MeasurementInputProbabilityOfPaymentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_MeasurementInputPaymentDiscountRateMember" abstract="true" name="MeasurementInputPaymentDiscountRateMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_SaleOfMarketableSecurities" abstract="false" name="SaleOfMarketableSecurities" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_InventoryCurrentAndNoncurrent" abstract="false" name="InventoryCurrentAndNoncurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_NucyntaMember" abstract="true" name="NucyntaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour" abstract="false" name="FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_AccruedProductTaxesAndFeesCurrent" abstract="false" name="AccruedProductTaxesAndFeesCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_AccruedPayablesForInventoryCurrent" abstract="false" name="AccruedPayablesForInventoryCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_AccruedIncentiveCompensationCurrent" abstract="false" name="AccruedIncentiveCompensationCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_AccruedLiabilityForCashSettledShareBasedAwardsAssumedFromAcquireeCurrent" abstract="false" name="AccruedLiabilityForCashSettledShareBasedAwardsAssumedFromAcquireeCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_TermLoan2024Member" abstract="true" name="TermLoan2024Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_DebtModificationAndTransactionFee" abstract="false" name="DebtModificationAndTransactionFee" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_DebtInstrumentCommitmentAndOtherFees" abstract="false" name="DebtInstrumentCommitmentAndOtherFees" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_ProceedsFromTermNoteModification" abstract="false" name="ProceedsFromTermNoteModification" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_DebtInstrumentEarlyMaturityThresholdConvertibleNotesOutstandingPrincipalBalance" abstract="false" name="DebtInstrumentEarlyMaturityThresholdConvertibleNotesOutstandingPrincipalBalance" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_DebtInstrumentEarlyMaturityThresholdLiquidity" abstract="false" name="DebtInstrumentEarlyMaturityThresholdLiquidity" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_DebtDiscountAndIssuanceCostsIncurredAndIncludedInExtinguishmentOfDebt" abstract="false" name="DebtDiscountAndIssuanceCostsIncurredAndIncludedInExtinguishmentOfDebt" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_DebtInstrumentFinancialCovenantCashNettingLimit" abstract="false" name="DebtInstrumentFinancialCovenantCashNettingLimit" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_ContractualInterestExpense" abstract="false" name="ContractualInterestExpense" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_DebtInstrumentConvertibleConsecutiveBusinessDays" abstract="false" name="DebtInstrumentConvertibleConsecutiveBusinessDays" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="coll_DebtInstrumentConvertibleMeasurementPeriod" abstract="false" name="DebtInstrumentConvertibleMeasurementPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="coll_DebtInstrumentConvertibleThresholdPercentageOfProductOfSalePriceOfCommonStockAndConversionRate" abstract="false" name="DebtInstrumentConvertibleThresholdPercentageOfProductOfSalePriceOfCommonStockAndConversionRate" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="coll_DebtInstrumentDefaultPeriodOnPaymentOfInterest" abstract="false" name="DebtInstrumentDefaultPeriodOnPaymentOfInterest" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="coll_DebtInstrumentNumberOfCalendarDaysToCureDefaultAfterOccurrence" abstract="false" name="DebtInstrumentNumberOfCalendarDaysToCureDefaultAfterOccurrence" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="coll_DebtInstrumentDefaultProvisionTermOfNoticeToCompanyToSureDefault" abstract="false" name="DebtInstrumentDefaultProvisionTermOfNoticeToCompanyToSureDefault" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="coll_DebtInstrumentDefaultProvisionsThresholdAmountBorrowed" abstract="false" name="DebtInstrumentDefaultProvisionsThresholdAmountBorrowed" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_DebtInstrumentDefaultProvisionsThresholdAmountOfPayment" abstract="false" name="DebtInstrumentDefaultProvisionsThresholdAmountOfPayment" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_DebtInstrumentTotalMinimumPayments" abstract="false" name="DebtInstrumentTotalMinimumPayments" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_DeferredRoyaltyLiabilityTable" abstract="true" name="DeferredRoyaltyLiabilityTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="coll_NetSalesPriorToJuly12025Member" abstract="true" name="NetSalesPriorToJuly12025Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_NetSalesPriorAfterJuly12025AndUpToMarch2032Member" abstract="true" name="NetSalesPriorAfterJuly12025AndUpToMarch2032Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_DeferredRoyaltyLiabilityLineItems" abstract="true" name="DeferredRoyaltyLiabilityLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="coll_RoyaltyRatePercent" abstract="false" name="RoyaltyRatePercent" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="coll_DeferredRoyaltyObligationInterestRateEffectivePercentage" abstract="false" name="DeferredRoyaltyObligationInterestRateEffectivePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="coll_InterestExpenseOnDeferredRoyaltyLiability" abstract="false" name="InterestExpenseOnDeferredRoyaltyLiability" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_NetAccretionForDeferredRoyaltyObligation" abstract="false" name="NetAccretionForDeferredRoyaltyObligation" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_PaymentOfDeferredRoyaltyObligation" abstract="false" name="PaymentOfDeferredRoyaltyObligation" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_DeferredRoyaltyAcquiredRollForward" abstract="true" name="DeferredRoyaltyAcquiredRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="coll_DeferredRoyaltyLiabilityAccretionAmortizationNet" abstract="false" name="DeferredRoyaltyLiabilityAccretionAmortizationNet" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_StockIncentivePlan2014Member" abstract="true" name="StockIncentivePlan2014Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_EquityIncentivePlan2025Member" abstract="true" name="EquityIncentivePlan2025Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_AwardsGrantedPriorTo2025Member" abstract="true" name="AwardsGrantedPriorTo2025Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_AwardsGrantedAfter2025Member" abstract="true" name="AwardsGrantedAfter2025Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_ShareRepurchaseProgram202425Member" abstract="true" name="ShareRepurchaseProgram202425Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_AcceleratedShareRepurchaseProgramMay2025Member" abstract="true" name="AcceleratedShareRepurchaseProgramMay2025Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_ShareRepurchaseProgram202526Member" abstract="true" name="ShareRepurchaseProgram202526Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualAdditionalSharesAuthorizedAsPercentageOfOutstandingShares" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualAdditionalSharesAuthorizedAsPercentageOfOutstandingShares" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="coll_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardExercisePeriodAfterExpirationDate" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardExercisePeriodAfterExpirationDate" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="coll_PaymentsForRepurchaseOfCommonStockUpfrontPaymentPercent" abstract="false" name="PaymentsForRepurchaseOfCommonStockUpfrontPaymentPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="coll_StockRepurchasePricePerShare" abstract="false" name="StockRepurchasePricePerShare" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="coll_TreasuryStockSharesAdditionalReceived" abstract="false" name="TreasuryStockSharesAdditionalReceived" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="coll_TreasuryStockAcquiredFeesAndCommissionIncurred" abstract="false" name="TreasuryStockAcquiredFeesAndCommissionIncurred" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPerformanceAdjustment" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPerformanceAdjustment" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="coll_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedPerformanceAdjustmentsWeightedAverageGrantDateFairValue" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedPerformanceAdjustmentsWeightedAverageGrantDateFairValue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="coll_AwardsGrantedPriorTo2024Member" abstract="true" name="AwardsGrantedPriorTo2024Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_AwardsGrantedAfter2024Member" abstract="true" name="AwardsGrantedAfter2024Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_EquityInstrumentsOtherThanOptionsGrantsInPeriodWithMarketBasedVestingConditionsWeightedAverageGrantDateFairValue" abstract="false" name="EquityInstrumentsOtherThanOptionsGrantsInPeriodWithMarketBasedVestingConditionsWeightedAverageGrantDateFairValue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="coll_EmployeeStockPurchasePlanPurchasePricePercentage" abstract="false" name="EmployeeStockPurchasePlanPurchasePricePercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="coll_EmployeeStockPurchasePlanCompensationExpense" abstract="false" name="EmployeeStockPurchasePlanCompensationExpense" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_PurduePharmaLimitedPartnershipPatentInfringementMember" abstract="true" name="PurduePharmaLimitedPartnershipPatentInfringementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_PurduePharmaLimitedPartnershipPatentInfringementDistrictOfMassachusettsMember" abstract="true" name="PurduePharmaLimitedPartnershipPatentInfringementDistrictOfMassachusettsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_GrunenthalGMBGLitigationMember" abstract="true" name="GrunenthalGMBGLitigationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_BdsiAcquisitionLitigationMember" abstract="true" name="BdsiAcquisitionLitigationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_ArbitrationWithNorthSoundPharmaceuticalsIncMember" abstract="true" name="ArbitrationWithNorthSoundPharmaceuticalsIncMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_WalgreenCo.LawsuitMember" abstract="true" name="WalgreenCo.LawsuitMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_LossContingencyStayPeriodBeforeFinalFederalDrugAdministrationApprovalCanBeIssuedIfPatentInfringementLitigationElected" abstract="false" name="LossContingencyStayPeriodBeforeFinalFederalDrugAdministrationApprovalCanBeIssuedIfPatentInfringementLitigationElected" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="coll_StatutoryPeriodOfProceedings" abstract="false" name="StatutoryPeriodOfProceedings" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="coll_LossContingencyNumberOfAdditionalCasesFiled" abstract="false" name="LossContingencyNumberOfAdditionalCasesFiled" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="coll_LossContingencyNumberOfDemandLettersReceivedFromPurportedStockholders" abstract="false" name="LossContingencyNumberOfDemandLettersReceivedFromPurportedStockholders" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="coll_AmortizationAndImpairmentOfIntangibleAssets" abstract="false" name="AmortizationAndImpairmentOfIntangibleAssets" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_SingleReportableSegmentMember" abstract="true" name="SingleReportableSegmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_CommercialExpenses" abstract="false" name="CommercialExpenses" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_CorporateExpenses" abstract="false" name="CorporateExpenses" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_MedicalExpenses" abstract="false" name="MedicalExpenses" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_TechnicalOperationsExpenses" abstract="false" name="TechnicalOperationsExpenses" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_OneLincolnLeaseMember" abstract="true" name="OneLincolnLeaseMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="coll_OperatingLeaseAreaOfLeasedSpace" abstract="false" name="OperatingLeaseAreaOfLeasedSpace" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:areaItemType"/>
  <xs:element id="coll_LesseeOperatingLeaseNumberOfRenewalOptions" abstract="false" name="LesseeOperatingLeaseNumberOfRenewalOptions" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="coll_OperatingLeaseRentExpenseBaseRentAnnual" abstract="false" name="OperatingLeaseRentExpenseBaseRentAnnual" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="coll_OperatingLeaseRentExpenseBaseRentAnnualIncreasePercent" abstract="false" name="OperatingLeaseRentExpenseBaseRentAnnualIncreasePercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
</xs:schema>
